Field of the Invention
The invention relates to a method for manufacturing an object by solidifying powder using a laser beam, with the insertion of a member for absorbing deformations.
Herein, the term powder should be understood to denote a powder or a powder mixture. This powder, or this powder mixture, may be mineral, for example ceramic, or metallic. The term solidification denotes a method for manufacturing an object by successively solidifying a plurality of overlaid layers of powder or powder mixture. These layers are previously spread and compacted on a plate acting as a work area. Each layer of powder, or powder mixture, is solidified at areas constituting the walls of the object, using a laser beam. Such solidification is also referred to as sintering and this term will be used hereinafter.
When manufacturing thick-walled and/or large objects, the appearance of some deformations may be observed. These deformations occur when the constituent material of the object, i.e. the solidified powder, has reached a certain temperature after treatment with the laser beam. The temperature reached in the layers of sintered powder constituting the walls of the object is dependent not only on the thermal energy provided by the laser beam but also on the thermal conductivity coefficient of the solidified powder. Furthermore, due to the size thereof, the shape thereof and/or the type of powder, the object has a given linear expansion coefficient. Insofar as the object is manufactured on a plate made of a rigid material, this plate also has a specific thermal conductivity coefficient and expansion coefficient.
During the production process, the object has a temperature varying in the course of production, i.e. it increases at each passage of the laser beam. In parallel with the temperature rise in the object, a temperature rise in the plate acting as the work surface is observed.
The temperature of the sintered object is, in principle, always greater than that of the plate since the object receives the energy emitted by the laser beam. If the expansion coefficient of the plate is greater than or equal to that of the object, a first type of deformation of the plate is observed. In this case, the plate has a surface, intended to be in contact with a complementary surface of the object, which is convex. This deformation of the plate impacts the object which thus exhibits complementary deformation, i.e. the object has at least one concave surface intended to be in contact with the convex face of the plate.
On the other hand, if the expansion coefficient of the object is greater than that of the plate, since the temperature of the object is always greater than that of the plate, another type of deformation is observed. In this case, at least one surface of the object, intended to be in contact with the plate, is concave. In this case, the plate exhibits complementary deformation, i.e. with at least one convex surface intended to be in contact with the object.
If the temperature of the object is less than that reached by the plate, regardless of the respective expansion coefficients of the object and the plate, deformation of one surface of the object intended to be in contact with the plate, which is convex whereas the complementary surface of the plate is concave, is observed.
Description of the Related Art
One of the known solutions for remedying these deformations is that of using, both for the plate and for manufacturing the object, materials wherein the thermal conductivity and/or expansion coefficients are sufficiently similar for the dimensional variations of the plate and the object to be equivalent. This is difficult to carry out since not all objects are made from powder having a similar expansion coefficient to that of the constituent material of the plate, at least in terms of mechanical properties. Furthermore, the temperatures of the object and the plate vary during the production process. For this reason, deformations may occur to varying degrees according to the temperatures.
EP-A-2 022 622 describes a method for manufacturing an object held in position in a frame, during the manufacture thereof, by braces having a complex shape arranged on the periphery of the object. These braces are not effective in preventing the appearance of deformations, insofar as the object retains a bottom wall surface in contact with the plate. Moreover, these braces require the use of a large volume of powder and a plate having relatively larger dimensions than those of the finished object, which is not satisfactory.